Electrical storage elements are, for example, capacitors or else rechargeable batteries. In particular, capacitors are used as storage elements in so-called intermediate circuits of e.g. inverters. In this case, they can have high charge capacitances (e.g. 5 mF) and/or high voltages (e.g. 1000 V). For the exchange and maintenance thereof, therefore, it is necessary to discharge these electrical storage elements safely.
Discharge apparatuses are known from consumer electronics, but said discharge apparatuses are not suitable on account of the low charge capacitances that occur there. Discharge apparatuses for motor vehicle batteries likewise cannot be used on account of their slowness.
So-called “kludges” are often used as well, in particular simple power resistors, which, for discharging an electrical storage element, are connected directly to the latter, e.g. to a capacitor. However, said power resistors on the one hand have to be designed for the high powers that occur (high weight and corresponding size), and on the other hand can heat up greatly or explode, particularly if the current feed to the electrical storage element to be discharged was not interrupted (e.g. in the case of a non-disconnected photovoltaic (PV) generator at the intermediate circuit of an inverter) and a continuously high current therefore flows through this bridging load resistor. Moreover, current accidents can occur, if, if appropriate, insulations melt as a result of high heating and voltage-carrying conductors become touchable.
The patent specification DE 195 13 441 C5 describes a circuit arrangement for testing electrical operating equipment, in particular a power cable with a high internal capacitance. The circuit arrangement is designed to supply a varying voltage to a test specimen according to a given voltage vs. time curve. For this purpose, the circuit arrangement comprises two variable DC power sources for providing a positive and a negative voltage, respectively. Furthermore, a controlled electronic high-voltage switch and a load resistor connected in series with the switch are provided for discharging the internal capacitance of the specimen. The interaction of the DC power sources for charging the internal capacitance of the specimen and of the electronic high-voltage switch for discharging the specimen allows for an accurate tracing of the given voltage vs. time curve.
IBM Technical Disclosure Bulletin, Vol. 37, No. 06A, June 1984, discloses an electronic circuit for monitoring the temperature of a battery within a device and for adjusting the charge and discharge rates according to the measured temperature. That way, maximum utilization of the device is provided while maintaining safe conditions at the battery.
Patent application DE 102 61 118 A1 discloses a battery charger that applies short intermediate discharge cycles at regular intervals to a battery while charging it. The intermediate discharge cycles remove depositions from electrodes of the battery, thereby increasing the lifetime of the battery.